Harry Stern, a polar scientist at the University of Washington’s Applied Physics Laboratory, has been studying the Arctic Ocean for decades, and sailed part of the Northwest Passage in 2009. Stern’s latest work uses the earliest explorers’ experiences to better understand a maritime environment that still contains many unknowns. A paper published in November in Polar Geography uses Captain James Cook’s records of sea-ice edge, more than two centuries ago, as a way to understand the changes we’re seeing now. UW Today asked him a few questions about the project.

How did you come to publish a paper about this historical map of Arctic sea ice?

It started when I was writing a book chapter called “Sea Ice in the Western Portal of the Northwest Passage from 1778 to the 21st Century” for a book by University of Washington Press. In the course of researching Cook’s 1778 foray into the Arctic, I realized that he had sailed close to the ice edge, and that his officers had made detailed charts of their positions. It didn’t take long to figure out that these were the earliest historical records of the ice edge in the Chukchi Sea.

Detail from Henry Roberts’ chart of the NW Coast of America and the NE Coast of Asia. The red line shows the approximate ice edge that caused Captain James Cook to turn back.Harry Stern/University of Washington

Where did you find the map?

The definitive versions of Captain Cook’s journals were published in several volumes in the 1950s and 1960s. Accompanying them is a large-format collection, “Charts & Views Drawn by Cook and his Officers and Reproduced from the Original Manuscripts.” Both are available at Suzzallo Library. In looking through the large-format collection, I found the chart by naval officer Henry Roberts that became Figure 1 of my paper. The figure is actually just a portion of his original chart.

To learn more about it, I went to UW Libraries Special Collections and found “The Charts and Coastal Views of Captain Cook’s Voyages,” which had a lot of useful information, including reproductions of other charts made by Cook and his officers. There I also found a first edition, from 1784, of the published account of Cook’s third voyage. The original charts from that voyage are in various places around the world, including the U.K. and Australia, so I have not yet seen an original chart.

You note that the ice has been quickly retreating since the 1990s. Why have we only begun to see this in recent decades?

For hundreds of years — or maybe longer — the ice edge in the Chukchi Sea in August varied from year to year, but on average it was more or less where Cook found it in August 1778. With global warming, things began to change, but the cumulative effect before the 1990s was not noticeable above the year-to-year variability inherent in the system. Sometime in the 1990s the “signal” began to emerge from the background “noise” — that is, the northward retreat of the ice edge became larger than the typical year-to-year variability of the August ice edge. That’s when we started to notice that things were changing.

What strikes you most about the changes to Arctic sea ice since Cook’s failed voyage?

In the last 10 to15 years, the changes have been dramatic. The summer ice edge in the Chukchi Sea is now hundreds of miles farther north than it used to be. This has opened up the opportunity for many ships, mostly private yachts, to transit the Northwest Passage, and for oil companies to consider drilling in the Chukchi Sea. It’s also impacting ice-dependent marine mammals like polar bears and beluga whales. But one thing hasn’t changed: it’s still dangerous to navigate through ice-covered waters.

When will the Arctic Ocean be ice-free in summer, and when might the Northwest Passage be used for navigation?

Climate models predict a nearly ice-free summer Arctic Ocean by about 2060, but with a large spread among models (some predict decades earlier, some decades later). However, the actual observational record over the last 35 years shows that most models are too conservative and that a nearly ice-free summer Arctic Ocean is more likely to arrive in the 2020 to 2040 timeframe. Note that “nearly ice-free” is commonly used to mean that the ice extent in the Arctic Ocean is 1 million square kilometers or less. This compares with 7 to 8 million square kilometers for the summer sea-ice extent before the year 2000, and about 5 million sq. km in more recent years.

A chart of trips made through the Northwest Passage.Harry Stern/University of Washington&Bob Headland/University of Cambridge

The Northwest Passage is a long and complex series of channels and waterways that wind through the Canadian Arctic Archipelago. While the Northwest Passage has been open in recent summers to small boats and occasional cruise ships, it is not yet a commercially viable shipping route, for several reasons: ice can still be a hazard, the route is shallow and narrow in places, there are very few aids to navigation and there is no search-and-rescue capability in place.

I wouldn’t expect the Northwest Passage to become a major commercial shipping route anytime soon. On the other hand, the Northern Sea Route, which passes along the north coast of Russia, has been handling an increasing amount of commercial traffic in recent years and is probably a more viable shipping route. The Northwest Passage will continue to see more “destinational” shipping (e.g., to a northern port and then out by the same route) and more small-boat traffic.

Does anything else strike you about this map?

The chart included as Figure 1 in my paper is interesting beyond the fact that one can deduce the approximate sea-ice edge from it. It contains a handwritten note by William Bligh calling attention to a “gross mistake” in which the same island has been plotted as two separate islands. Bligh writes: “How they have blundered to lay them down as two I cannot conceive.” Bligh was an officer on Cook’s third voyage, 1776-1780, but he is better known in connection with the mutiny on the HMS Bounty in 1789.

The chart also contains the handwritten word “Lisburne” at the site of Alaska’s modern-day Cape Lisburne, but it is not known who wrote that word on the chart, nor who came up with the name. Details like that add interest to the chart.